Preparation of light-developable,direct-writing silver halide emulsions by rapid precipitation and long ripening

ABSTRACT

LIGHT-DEVELOPABLE, DIRECT-WRITING RADIATION-SENSITIVE SILVER HALIDE EMULSIONS HAVING REDUCED PHOTOLYZED IMAGE ACCESS TIME AND IMPROVED SENSITOMETRIC PROPERTIES ARE PREPARED BY PRECIPITATING SILVER CHLORIDE IN NOT MORE THAN 3 MINUTES IN THE PRESENCE OF 10 TO 20 MOLE PERCENT BASED ON SILVER OF A WATER-SOLUBLE PLUMBOUS SALT IN AN ACIDIFIED AQEOUS COLLOID SOLUTION, CONVERTING THE SILVER CHLORIDE TO SILVER BROMIDE BY ADDING A STOICHIOMETRIC EXCESS OF A WATER-SOLUBLE BROMIDE SALT AND SLOWLY RIPENING THE EMULSION BY HEATING AT ABOUT 150-180* F. FOR AT LEAST 3 HOURS WHILE ADDING 10 TO 20 MOLE PERCENT OF A SEPARATE FINE GRAIN SILVER BROMIDE. THE EMULSION IS WASHED AND REDISPERSED, AND A HALOGEN ACCEPTOR ADDED ALONG WITH OTHER FINAL ADJUVANTS PRIOR TO COATING.

United States Patent Int. Cl. G03c 1/02 U.S. 'CI. 96-94 10 Claims ABSTRACT OF THE DISCLOSURE Light-developable, direct-writing radiation-sensitive silver halide emulsions having reduced photolyzed image access time and improved sensitometric properties are prepared by precipitating silver chloride in not more than 3 minutes in the presence of 10 to 20 mole percent based on silver of a water-soluble plumbous salt in an acidified aqueous colloid solution, converting the silver chloride to silver bromide by adding a stoichiometric excess of a water-soluble bromide salt and slowly ripening the emulsion by heating at about 150180 F. for at least 3 hours while adding 10 to 20 mole percent of a separate fine grain silver bromide. The emulsion is washed and redispersed, and a halogen acceptor added along with other final adjuvants prior to coating.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a process for making lightdevelopable, direct-Writing, oscillographic-recording silver halide emulsions, layers, and elements having improved photolyzed image access time and improved sensitometric characteristics.

Description of the prior art Light-developable, direct-writing oscillographic recording elements are described in U.S. Pats. 3,033,678; 3,033,- 682; 3,178,293; 3,183,088; 3,189,456; 3,249,440 and others. In these patents it is taught to prepare direct-writing emulsions by carrying out the initial precipitation of the silver halide by slowly adding aqueous silver nitrate to an acidified aqueous gelatin solution of a water soluble halide, usually a chloride. The period of addition is usua1- ly about 20 minutes or more and it may be carried out in the presence of a small amount of a Water-soluble plumbous salt (e.g., 0.5 to 5 mole percent based on the silver). If the initial halide is chloride, it is preferably converted to silver bromide by adding a stoichiometric excess of a water soluble bromide and ripening the emulsion for about 40 minutes. The emulsion is washed and redispersed, e.g., in a manner described in Moede, U.S. Pat. 2,772,165. A halogen acceptor, e.g., stannous salt, is added and the emulsion digested and after the addition of final adjuvants, e.g., hardeners, butters, etc. the emulsion is coated.

A disadvantage of the previous direct-writing layers is that image access time is excessive. That is, the time interval between when the high intensity light trace is recorded, and when the trace image becomes visible under exposure to light-developing lower intensity radiation, is long. It is a major objective of these direct-writing papers to make the image visible by light development in the least amount of time possible. The use of a plumbous salt during the precipitation of the silver halides produces higher speed and maximum density and improves image and aging stability as compared to adding it at the time of digestion or just before coating along with the halogen acceptor. However, it does tend to produce a higher background density which tends to extend image access time.

SUMMARY OF THE INVENTION This invention pertains to a process for making a lightdevelopable, direct-writing colloid silver halide emulsion having reduced background, improved contrast, higher maximum density and greatly reduced image access time. It has been assumed in this art that it is advantageous to form the silver halide grains slowly and to form large grains in this manner to obtain the best sensitometric characteristics for direct writing papers. It has now been found that smaller grains formed by rapid precipitation of silver chloride in the presence of from 10 to 20 mole percent of plumbous ions, bromide conversion and, long ripening at high temperatures provides :the above advantages. In general, the process comprises:

(1) Precipitating silver chloride in an aqueous acidified solution of a water-permeable organic colloid binding agent in a period of not more than 3 minutes in the presence of 0.1 to 0.2 mole of a water-soluble plumbous salt per mole of silver at approximately 150180 F.;

(2) Adding rapidly at least 2 times the stoichiometric amount of a water-soluble inorganic bromide necessary to convert the silver chloride to silver bromide, ripening the emulsion by heating it to about 150 to 180 F. for at least 3 hours, and preferably adding from 0.1 to 0.2 mole of fine grain silver bromide per mole of originally precipitated silver during this ripening period;

(3) Washing the emulsion with an aqueous solution to remove soluble salts;

(4) Redispersing the emulsion in an aqueous medium and if desired, adding more water-permeable colloid, digesting the emulsion at about to 140 F. for 5 to 30 minutes and, during digestion or prior to coating, adding, based on silver,

(a) 0 to 5 mole percent of a water-soluble plumbous or cupric salt,

(b) 0 to mole percent of a water-soluble inorganic bromide,

(c) a halogen acceptor.

After digestion, the emulsion is cooled to coating temperature, buffers and coating aids added, and the emulsion coated on a suitable support to provide about 18 to about 55 mg. of silver bromide per square decimeter.

The precipitation can be accomplished using any of the water-soluble silver salts and water-soluble halides described in the patents listed above but is preferably carried out as claimed in U.S. 3,178,293 by admixing silver nitrate and a plumbous salt in an aqueous solution with an aqueous acidified solution of the colloid and a watersoluble halide. The water-soluble halide is preferably chloride but may contain small amounts of iodide and/or bromide ions. Suitable acids are hydrochloric, nitric, and organic acids, e.g., citric, acetic, chloroacetic or bromoacetic acid.

Step (3) can be carried out by forming noodles and washing them, and by the coagulation and washing treatment described in Moede U.S. Pat. 2,772,165, Nov. 27, 1965, especially in Example I, or in other manners.

. The important aspect of the process of the invention involves the rapid precipitation of silver halide in the presence of plumbous ions to produce fine grains in which the lead is adsorbed to the silver halide grains and this is believed to restrain Ostwald ripening. By long ripening at high temperature in a high potassium bromide solvent atmosphere, the crystals finally become larger by coalescence. This appears to promote greater photolytic sensitivity. The addition of fine grain silver bromide to the system during ripening produces greater photolyzed density. Optical sensitizing dyes may be added just prior, during or after digestion or just prior to coating.

The halogen acceptors include stannous chloride, salts providing iodide and thiocyanate ions, molecular iodine, alkali metal nitrites, phenylenediamines, aminophenols, hydroquinone, and 3-pyrazolidones, but other known halogen acceptors can be used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred halogen acceptors for this invention are potassium iodide and stannous chloride. In general, from 0.5 to 120 mole percent and preferably to 40 mole percent of a stannous salt based on the silver may be used or 0.2 to 2.0 mole percent of potassium iodide may be used. Rapid precipitation of silver chloride in the presence of 0.1 to 0.2 mole of plumbous salt, rapid conversion to silver bromide by the addition of at least 2 times the stoichiometric amount to convert the silver chloride to silver bromide and long ripening of the emulsion at high temperature with the addition of fine grain silver bromide during this period are the basic preferred steps to give direct writing papers of high quality. After the addition of the halogen acceptor and the digestion step, the usual coating adjuvants, e.g., hardeners, wet ting agents, etc. are added and the viscosity is adjusted by the addition of a further quantity of gelatin or other colloid. In general, the ratio of gelatin to silver halide is 2:1; however, this is not at all critical. The prepared emulsion is then coated on a suitable support, e.g., paper and dried to give a dry coating weight equivalent to about 18 to about 55 mg. AgBr/dm To determine the sensitometric characteristics of the direct writing material it may be exposed through a power of 2 step wedge in an electronic flash tube sensitometer similar to that described by Wyckoff and Egerton, Journal of the Society of Motion Picture and Television Engineers, 66, 474 (1957). This instrument has a zenon discharge tube as the source of radiation and has available two exposure times of and 1000 microseconds. The exposed material may be light developed by irradiation under cool white fluorescent lighting at about 95 foot-candle intensity. To determine the densities of the image and background, a reflection densitometer may be used whose values correspond to visual density. To test image access time, the material was exposed at 0.0001 sec. on an Edgerton, Germeshausen and Grier Mark VI sensitometer and light developed by irradiation under the cool white fluorescent lighting described above. An arbitrary numerical designation of the time necessary for the image to appear is given with number -1 being the fastest.

The following examples further illustrate but are not intended to limit the scope of the invention.

EXAMPLE I An emulsion was made in the following manner.

(A) In a total volume of 1666 ml. of an equeous solution, there were dissolved 1.0 mole of potassium chloride, quantities of plumbous nitrate according to the table below, 33.3 grams of inert gelatin. The temperature was adjusted to 160 F. and the pH to 2.0 with approximately .05 mole of hydrochloric acid.

(B) In a total volume of 666 ml. of an aqueous solution there were dissolved 1.0 mole of silver nitrate and quantities of plumbous nitrate according to the table below.

(C) While rapidly strring, the silver nitrate solution was added to the aqueous gelatin silver chloride solution in 60 seconds or less.

(D) In one minute there was added 3.2 moles of potassium bromide dissolved in 1066 ml. of water. The resulting mixture was held at 160 F. for 5 hours. Four hours after starting the bromide conversion, in 30 seconds add 0.12 mole of fine grain silver bromide prepared by precipitating on a mole for mole basis in an acidified aqueous gelatin solution silver nitrate and potassium bromide.

(E) The resulting emulsion was coagulated and washed as described in Examples I of Moede 2,772,165 and redispersed.

(F) To the redispersed emulsion there were added suflicient gelatin to provide a concentration of about 5-6%, the optical sensitizing dye disclosed below in Example VI, 2'mole percent potassium bromide and 20 mole percent stannous chloride based on the silver halide present in the system.

The silver halide emulsion was digested at 130 F. for minutes. After digestion, the emulsion was cooled to coating temperature, buffers and coating aids were added, and the emulsion was coated on a suitable paper support to provide approximately mg. of silver bromide per square decimeter, and dried in a conventional manner.

The resulting material was tested as described above and the results are shown in the following Table I which illustrates that from 0.01 to 0.2 mole of plumbous ion per mole of silver provides improved maximum density and low background density.

TABLE I.AMOUNT OF Pb+ [Precipitation Variation] Moles Pb lmole Ag+ Test method #1 Soluble (a) (b) halide In Ag+ soln. soln. Total Speed Access D-max. Bkgd 1 Test Method #1: Expose on Edgerton, Germeshausen and Grier Sensitorneter at 0.0001 see. thru a power of 2 step Wedge. Photolyze (a) at 110 it. candles daylight fluorescent light for 2 min. Photolyze (b) ft. candle daylight fluorescent light for 4 min. and read densities on a reflection densitometer.

Speed=number of wedge steps visible in which a larger number indicates greater speed.

Access=An arbitrary rating in which #1 is fastest.

Backgrouud=Density difierence between white paper and photolyzed sample where no imaging exposure was given.

D-max.=Density diirerenee between background and maximum image density.

EXAMPLE II AgCl Precipitation time Emulsions were made as described in Example I except that .04 mole of plumbous nitrate was incorporated in the gelatin potassium chloride solution and 0.1 mole was incorporated in the silver nitrate solution and AgCl precipitation time was varied as described in Table II. When the emulsions were remelted in the Sh system described earlier and tested, the results shown in Table II illustrate that both speed and access are improved by precipitation in 2 min. or less. It is preferred to use sec. or less because of the resulting reduced background. Coatings 1 and 2 were both included to show that with slow AgCl precipitation, speed and access were not altered by presence or absence of fine grain AgBr.

TABLE II.PRECIPITATION TIME OF AgCl [Precipitation Variations] Test method #1 (see Ex. I)

Moles AgCl fine (a) (b) pptn. grain Coating No. time AgBr Speed Access D-max. Bkgd.

20 min None 7 2 28 15 20 min .14 7 2 .30 .16 33 sec"--. .14 10+ 1 .32 .09 44sec .14 l1 1 .35 .12 71 sec .14 10 1 .33 .18 75sec .14 10 1 .33 .15 87sec .14 10 1 .33 .17 sec c .14 10 1 .31 .20

EXAMPLE III Ripening time with KBr Emulsions were made as described in Example I except that .02 mole of Pb+ were used in the gelatin soluble halide solution, none with the silver nitrate solution, and the KBr ripening time was varied as described in Table III. When the emulsions were remelted in the Sn+ system described above, the results shown in Table III illustrate that a 3 hr. or longer ripening time is useful, but a 5 hr. ripening time is preferable.

TABLE III.RIPENING TIME WITH KBr Test Method #1 (see Ex. I)

TABLE V.AMOUNT OF FINE GRAIN AgBr Emulsions were made as described in Example I except that .0133 mole of Pb+ were used in the gelatin/soluble halide solution and 0.1 mole in the silver nitrate solug gg Q 15 tion and the fine grain AgBr addition time was altered Coating No. time, min. Speed Access D-max. Bkgd as described in Table VI. These emulsions were remelted 10 6 3 .43 in the Sn+ system, with and without sensitizing dye. 20 s 3 .13 .42 Test results given in Table VI show that sensitizing dye 58 3 g j: jg increases speed, and that fine grain AgBr increases D-max, 15 8-1 but that the time of addition of the fine grain AgBr matters little. A 4-hr. period for addition is preferred.

TABLE VL-TIME FINE GRAIN AgBr ADDED f Precipitation variation Moles Time fine Test method #1 (see Ex.I)

fine gram AgBr Remelt gram added after variation (2) (b) AgBr/ converting Coating No. moleAg+ KBr Sens.* dye Speed Access D-max. Bkgd.

S-ghyl-dihydrobenz0xazoly1idine-2=5-isopropylidene-3-ethyl-2-thio-4-keto-tetrahydrooxazo EXAMPLE IV EXAMPLE VII Amt. of Test method #1 (see Ex. I) converting KBr/mole (a) (b) Ag+ in silver Coating No. soln., moles Speed Access D-max. Bkgd.

EXAMPLE V Emulsions were made as described in the preferred method using 0.04 mole of lead in the gelatin/soluble halide solution and 0.1 mole of lead in the AgNO solution except that the amount of fine grain AgBr added during bromide ripening was varied as described in Table V. When the emulsions were remelted in the Sn+ system described earlier and tested, the results shown in Table V illustrate that fine grain AgBr is useful in producing greater D-max. 0.143 mole AgBr/mole Ag+ in silver solution is preferred.

An emulsion was made according to Example I up to step F except that 0.0133 mole of plumbous nitrate was used in the gel salt and 0.1 mole in the silver nitrate solution. The fine grain silver bromide addition was carried out as indicated in the following table.

The emulsion was redispersed after the washing step E and sufiicient gelatin was added to provide the desired viscosity. The emulsion was optically sensitized with the dye of Example VI and there was then added 0.33 mole percent of potassium iodide based on the silver halide. The emulsion was digested at F. for 20 minutes and then cooled to coating temperature and coated on a support. The sensitometric results are shown in the following table.

TABLE VII Moles fine Time fine Test method #1 (see Ex. 1) grain grain AgBr AgBr] added after (a) (b) mole converting Ag+ KBr, hr. Speed Access D-max. Bkgd.

None 10+ 1 28 09 14 2 10+ 1 29 11 14 4 10+ 1 28 11 Stannous chloride, when used as a halogen acceptor, may be added from aqueous solution, particularly when such solutions are made using the anhydrous stannous compound. However, the stannous salt may also be added from ethanol, 2-ethoxyethanol, glycerine, dilute hydrochloric acid, etc.

Where it is desired, other halides or combinations of halides may be used to form the silver halide grains. For example, pure silver chloride, silver chlorobromide or silveriodochloride may be used. When soluble chloride salts are used, it is desirable, because of solubility difierences, to form the silver halide grains of desired size and then add sufficient soluble bromide salts to provide the desired concentration of bromide ions.

Other optical sensitizing dyes in addition to these are disploced in Example VI above may be used in the emulsions as well as convention antifoggants and coating aids.

In pace of the gelatin binding agent used in the foregoing examples there can be substituted other natural or synthetic water-permeable organic colloid binding agents, including the binding agents listed in Hunt, US. 3,033,682.

Suitable supports for the photographic emulsions made by the novel process of the invention include those used in the prior art on oscillographic recording elements. The preferred support is a photographic grade paper but it may be a hydrophobic film composed of a cellulose ester, e.g., cellulose acetate or a polymer, e.g., polyester films disclosed in Alles et al., US. 2,627,088 and Alles, US. 2,779, 684.

The novel process of this invention produces lightdevelopable, direct-writing, radiation-sensitive emulsion layers and elements having several advantages over the prior art materials. The emulsion layers and elements upon exposure to high intensity radiation and subsequent light-development, yield images of high maximum density and good stability against image fading. In addition, the image access time is greatly reduced as compared to the recording elements of the prior art. The elements are extremely convenient to use because wet processing can be eliminated, However, the elements are adaptable to conventional chemical development and fixing when a halogen acceptor other than tin is used. When tin is used as a halogen acceptor, an acid developer may be used to develop the image. The elements may be subjected to relatively high intensity illumination for long periods of time without substantial change in the image characteristics. The elements can be used to reproduce photographically the image record by high-intensity exposing radiation and without serious image deterioration. The elements have high photographic speed and contrast and, in addition, they have the ability to produce a useful image using relatively high intensity photolyzing light.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for making a light-developable, directwriting, water-permeable organic colloid emulsion which comprises (1) precipitating silver chloride from water-soluble silver salts and a water-soluble inorganic chloride in an acidified aqueous solution of a water-permeable organic colloid binding agent during a period of not more than 3 minutes and in the presence of 0.1 to 0.2

mole of a water-soluble plumbous salt per mole of silver at 150 F. to 180 F.;

(2) adding rapidly to the resulting aqueous emulsion at least 2 times the stoichiometric amount of a watersoluble inorganic bromide necessary to convert the silver chloride to silver bromide and ripening the emulsion by heating it to about 150 F. to 180 F. for at least 3 hours;

(3) washing the emulsion with an aqueous solution to remove soluble salts;

(4) redispersing the emulsion in an aqueous medium and adding more water-permeable organic colloid binding agent and digesting the resulting dispersion at about F. to 140 F. for about 5-30 minutes, and prior to any coating step, adding based on the silver;

(a) 0 to 5 mole percent of a water-soluble plumbous or cupric salt,

(b) 0 to mole percent of a water-soluble inorganic bromide, and

(c) a halogen acceptor.

2. A process according to claim 1, wherein said colloid is gelatin.

3. A process according to claim 1, wherein said watersoluble silver salt of step (1) is silver nitrate.

4. A process according to claim 1, wherein said watersoluble silver salt of step (1) is silver nitrate and said water-soluble chloride is potassium chloride.

5. A process according to claim 1, wherein said watersoluble bromide of step (2) is potassium bromide.

6. A process according to claim 1, wherein the halogen acceptor of step (4) is stannous chloride.

7. A process according to claim 1, wherein the plumbous salt is plumbous nitrate.

8. A process according to claim 1, wherein an optical sensitizing dye is added.

9. A process according to claim 1, wherein the emulsion was coagulated just before the washing step.

10. A process according to claim 1' wherein 0.1 to 0.2 mole of fine grain silver bromide per mole of originally precipitated silver is admixed during step (3).

References Cited UNITED STATES PATENTS 3,449,125 6/1969 Bigelow 96-108 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JR., Assistant Examiner US. Cl. X.R. 96108 

